cma.fitness_transformations.Function

a declarative base class, indicating that a derived class instance "is" a (fitness/objective) function.

A callable passed to __init__ is called as the fitness Function, otherwise the _eval method is called, if defined in the derived class, when the Function instance is called. If the input argument is a matrix or a list of vectors, the method is called for each vector individually like _eval(numpy.asarray(vector)) for vector in matrix.

>>> import cma
>>> from cma.fitness_transformations import  Function
>>> f = Function(cma.ff.rosen)
>>> assert f.evaluations == 0
>>> assert f([2, 3]) == cma.ff.rosen([2, 3])
>>> assert f.evaluations == 1
>>> assert f([[1], [2]]) == [cma.ff.rosen([1]), cma.ff.rosen([2])]
>>> assert f.evaluations == 3
>>> class Fsphere(Function):
...     def _eval(self, x):
...         return sum(x**2)
>>> fsphere = Fsphere()
>>> assert fsphere.evaluations == 0
>>> assert fsphere([2, 3]) == 4 + 9 and fsphere([[2], [3]]) == [4, 9]
>>> assert fsphere.evaluations == 3
>>> Fsphere.__init__ = lambda self: None  # overwrites Function.__init__
>>> assert Fsphere()([2]) == 4  # which is perfectly fine to do

Details:

• When called, a class instance calls either the function passed to __init__ or, if none was given, tries to call any of the function_names_to_evaluate_first_found, first come first serve. By default, function_names_to_evaluate_first_found == ["_eval"].
• This class cannot move to module fitness_functions, because the latter uses fitness_transformations.rotate.